1. Field of the Invention
The present invention relates to electrical switches generally and, more particularly, but not by way of limitation, to a novel hermetically sealed electrical switch having a high cycle life.
2. Background Art
Electrical switches are widely used to make and/or break electrical contacts. In some applications, aircraft and spacecraft, for example, it is desirable that the switching components be isolated from the surrounding environment.
The basic problem which the designer of any sealed switch must address is that switching motion must take place across a some type of sealing member in order to actuate the switch. Some attempts to fabricate such switches involve the use of sealing members such as silastic (rubber) boots, bellows, hoses, or diaphragms, with the required switching motion causing the sealing member to stretch or flex.
Some attempts to provide sealed switches include the following:
U.S. Pat. No. 2,777,910, issued Jan. 15, 1957, to Jordan et al., and titled HERMETICALLY SEALED SWITCH, describes a sealed snap switch in which the actuator operates across a diaphragm. PA1 U.S. Pat. No. 2,854,536, issued Sep. 30, 1958, to Beer, and titled SNAP-ACTION ELECTRIC SWITCHES, describes a sealed snap switch having a bellows-sealed actuator, the bellows including an internal spring to cause it to return to an extended position. PA1 U.S. Pat. No. 4,540,864, issued Sep. 10, 1985, to Krasser et al., and titled ACTUATING FIXTURE FOR PUSH-PULL SWITCH, describes an actuator for a push-pull switch which includes a "hose" (bellows) seal. PA1 U.S. Pat. No. 4,654,706, issued Mar. 24, 1987, to Rao et al., and titled DOUBLE-POLE SWITCH CONSTRUCTION, describes a sealed switch which is activated by pressing buttons formed on a flexible rubberized cover. PA1 U.S. Pat. No. 5,164,561, issued Nov. 17, 1992, to Schaeffeler et al., and titled PUSH BUTTON SWITCH HAVING SEALING BELLOWS, describes a switch having an actuator which is sealed with a bell shaped bellows. PA1 U.S. Pat. No. 5,382,767, issued Jan. 17, 1995, to Takano et al., and titled PUSH-BUTTON SWITCH, describes a switch having a bell shaped bellows disposed over an actuator button. PA1 U.S. Pat. No. 5,626,222, issued May 6, 1997, to Aguilera, and titled FORCE CONTROLLABLE SHIELDED MECHANICAL SWITCH ACTUATORS, describes a switch having an actuator which is formed internally of and integrally with a vertical metal bellows, the actuator depending from the upper wall of the bellows.
None of the foregoing switches, except for the one described in the '910 patent, is considered to a hermetically sealed switch and that one employs a flexing thin plate diaphragm. This provides a satisfactory seal, but the flexing thin plate diaphragm limits the mechanical life of the switch.
No known switch is presently offered that guarantees over 100,000 switching cycles.
Accordingly, it is a principal object of the present invention to provide a hermetically sealed electrical switch that has long electrical and mechanical life.
It is a further object of the invention to provide such a switch that meets stringent leak rate standards.
It is an additional object of the invention to provide such a switch that can be economically manufactured.
It is another object of the invention to provide such a switch that meets military standard MIL-S-8805, Enclosure 5, which states that an electrical switch construction must have a leak rate of no greater than 1.times.10.sup.-8 atm.cc/sec.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.